According to Hallick (1995), Deoxyribonucleic acid (DNA) is defined as a nucleic acid containing the genetic instructions that are used in the functioning and development of all living creatures except the RNA viruses. DNA molecules play a very significant role as a long-term storage of genetic information and they are related to a set of blueprints just like a code or a recipe, as the stored instructions are used in the construction of other cellular components such as RNA molecules and proteins. The genetic information is carried within the DNA segments called genes, but it has been found that other DNA sequences play a role in structural purposes, and can be concerned in regulating the utilization of the stored genetic information (Hartl, 2009). It is therefore very important to consider the structure of a DNA molecule as well as it replication process.
A DNA molecule is comprised of two simple units called nucleotides. Nucleotides are two long polymers that consist of backbones which are made up of phosphate groups and sugars put together by ester bonds. The two strands of DNA are anti-parallel since they run in opposite directions to one another. Within the structure of DNA there are four types of molecules known as bases and one of the four types of molecules is attached to each sugar in the backbone. The sequence of these four bases along the DNA's backbone encodes information and therefore enhancing development and functioning of living creatures (Hallick, 1995). The eukaryote organisms such as plants, animals, protists, and fungi store most of their DNA molecules within the cell nucleus while the rest of these molecules are stored in cell organelles for instance, chloroplasts or mitochondria. But prokaryote, such as archaea and bacteria store the DNA molecules within the cytoplasm. DNA is organized into chromosomes which are long structures found in cells. The chromosomes get duplicated before cell division in a process that is referred to as DNA replication (Hartl, 2009).
According to Stille (2006), DNA replication is the foundation for biological inheritance and is a very important process that takes place in all living organisms and during which the DNA molecules are copied. Each of the two original strands in the DNA structure acts as a template over which a complementary strand is reproduced. Thus, in due course of DNA replication, a single double-stranded molecule of DNA produces two identical DNA molecules. Within the living cells, there are error toe-checking and proofreading mechanisms which are fundamental in ensuring an almost perfect DNA replication (Watson & Berry, 2003). In a living cell, DNA replication starts at particular locations within the genome referred to as origins. The DNA molecule is unwound at the origin and new strands are synthesized such that a replication fork is formed. A replication fork is a structure that is made by helicases, which are used in breaking the hydrogen bonds that hold the two strands of DNA together. An enzyme called DNA polymerase synthesizes new DNA molecules by adding nucleotides corresponding to the template strand. In addition to this enzyme, many other proteins are linked to the replication fork and help in the creation and continuation of DNA molecule synthesis (Stille, 2006).
The initiator proteins engage other proteins in the separation of DNA strands at the origins and this forms a bubble. The origins tend to be rich in thymine and adenine bases to help in the replication process, since the A-T base pairs consist of two hydrogen bonds. Strands that are rich in these nucleotides are usually easier to separate because there is a positive relationship between hydrogen bonds (Watson & Berry, 2003). By the time these strands are separated, the RNA primers are formed on the template strands. DNA replication is therefore very important to organisms as it is critical in the continuation of a species since it enable an organism to create its genetic code and let it move to the next generation.